Ceramic coatings and methods of formulation



July 15, 1958' J. v. LONG 2,843,507

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July 15, 1958 J. v. LONG 2,843,507

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' 8 Sheets-Sheet 4 QNN HNNNN nvvavmn John I./ Long ma as 351% w July 15,1958 Original Filed Dec. 10, 1049 V. LONG 8 Sheets-Sheet 5 11210111.COATINGS AND TEST A'1A 10m. mum 2121110 00mm *coA-rxm 7011211221022. ms'rmcxmss 1111mm. mesa ,(F) 1 (Minutes) (inches) A. u. 0. 1201 as 1010sum. $5 2200 .002 120 hours at 1600F Am 1010 S'IEEL $8 $29 2200 .003 72hours at 1600F AISI 1020 STEEL $8 $21. 2200 l 10 .003 72 hours at 1600FA1s1 010 51mm. 545 2100 20 .0015 72 hours at 1600F AISI 1030 $11.21 $312100 10 .0025 72 hours s5 1700F AISI 1.130 012. 11. $30 $31 2100 10 .00272 hours at i700F A131 347 s'mRL 51.1 31.2 1900 5 v .001 72 hours s11700F AISI 31.7 smzx. $38 1900 5 .0015 72 hours at 1800F A151 310 sum.s41 $1.3 1900 5 .002 72 hours at 1700? A151 314 mm. 81.1 51.3 2300 10.0015 72 hours at 1a00r A151 311, 52221 .00075 72 hours at 1s502 $202250 10 I mm l 39 $32 1900 5 .0015 72 hours at 1000! I155 (m 831. 205010 .001 72 hours at 1s50r 5-816 (Alleghow- $31. 2050 10 .001 72 hours at1850F Lunm) $41. 2100 3 vmlnun .0025 72 hours at 1800F $1.1. 2100 3 .7nsstsno 13 .0025 72 hours'sa: 850F Explanation of Coating Combinationsthen indicates double coat, single flring-,; 1.0., 58 applied, than $29applied, 0h

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John M Long July 15, 1958 J. v. LONG 2,843,507

CERAMIC commas AND METHODS OF FORMULATION Original Filed Dec. 15, 1949 aSheets-Sheet s Fig. 6

INVENTOR John M Long Jul 15, 1958 J. v, LQNG 2,843,507

CERAMIC COATINGS AND METHODS OF FORMULATION Original Filed Dec. 15, 19498 Sheets-Sheet 7 //v vew TOR John I! Lang jmww July 15, 1958 J. v. LONG2,343,507

CERAMIC COATINGS AND METHODS OF FORMULATION Original Filed Dec. 15, 19498 Sheets-Sheet 8 INVE/VT'OR John M Long 8, ww flw W United States PatentCERAMIC COATINGS AND METHODS OF FORMULATION John V. Long, San Diego,Calif., assignor to Solar Aircraft Company, San Diego, Calif., acorporation of California Continuation of application Serial No.133,045, December 15, 1949. This application August 31, 1953, Serial No.377,381

18 Claims. (Cl. 117129) The present discovery and invention relate toimproved compositions of matter and methods of their production, andmore particularly to new protective layers and coatings of the ceramicor enamel type for metals and alloys; said layers and coatings havingqualities of thinness, adherence,-thermal and mechanical shockresistance, and latitude and simplicity of coating formulation,heretofore unattainable in prior ceramic and enamel coatings.

Historically the origin of the art of enameling and ceramic coating ofmetals is lost in antiquity. Examples of enamel coated metal jewelrydate back to the fourth century B. C. For the past century commercialiron and sheet metal enameling for protective and ornamental purposeshas been. highly developed, and research in this field has beenparticularly active from the beginning of the present century, andrapidly accelerated in efiorts to meet the needs of the two world wars.

For a number of years the exhaust manifolds of cer tain automobileengines have been coated with the conventional type of glossy porcelainenamel to prolong their lives. These were, however, unsatisfactory forairplane exhaust manifolds which operated at temperatures of the orderof 1000 F.; and it accordingly became the practice to make airplaneexhaust manifolds of heat resistant nickel-chrome alloys.

Also since early in 1942 designers of high temperature systems,particularly jet engines, rockets, gas turbine powerplants, heatexchangers, etc., have encountered serious materials problems, becauseavailable metals and alloys lack corrosion and oxidation resistance inthe temperature range above 1500 F. The military needs and, rivalriesrequiring increased thermal efficiencies, and prolongation of the lifeof such high temperature devices, have created an additional urgentdemand for better materials and/ or methods by which currently usedmaterials can be protected in such uses. A solution of these problemsappeared to lie in developing high temperature protective ceramiccoatings with the required properties to increase corrosion andoxidation resistance, and to enhance metal stability at highertemperatures. In addition, it appeared that ceramic coatings could beused on low temperature alloys made of readily available materials,which normally lacked high temperature corrosion and oxidationresistance, to permit their substitution for strategic materials.

For some years past, intensive direct government and governmentsubsidized development and private development of such coatings has beenunder way both in this country and abroad. In this country suchdevelopments have been particularly active at the United States NationalBureau of Standards, the department of Ceramic Engineering of theUniversity of Illinois, the Ohio State University Research Foundation,Armour Research Foundation of the Illinois Institute of Technology,Rutgers University, Battelle Memorial Institute, New York State Collegeof Ceramics and others, in co-operation with the United States AirMateriel Command, United States Naval Research, the United States ArmyOrdnance de- 2,843,507 Fatented July 15, 1958 "ice s is partment andTank Automotive Center, the National Advisory Sommittee for Aeronautics,and the Porcelain Enamel Institute. These organizations haveinvestigated means of providing oxidation and corrosion resistance formetals and alloys by utilizing known principles of enamel formulation toextend the temperature range of previously developed enamels for lowtemperature applications.

In spite of the vast amount of research and development, including theextensive Government direct and subsidized research carried on in thisfield, the prior commercial enamel and ceramic coatings for metals havein general required the use of separate base coats to secure adherenceto the metal to be coated, and outer coatings to secure reasonableprotective properties, and require complex formulations withcomparatively thick applications, and the finished coatings haverelatively poor adherence, poor protective qualities particularly atelevated temperatures, and poor thermal and mechanical shock resistance.In particular, a strong persistent demand by designers of, lightweight,high power, high temperature equipment for coatings applied in very thinlayers (in the range of .0005 to .003 of an inch in thickness) whichhave high thermal and mechanical shock resistance, and which willprovide corrosion and oxidation protection for extended periods ofservice life at temperatures above 1500 F. has not been met by the priorart. Various prior efforts and failures to supply this demand even withthe extensive government subsidized research are noted in the papersread at the Conference on Ceramic Materials for Application to AircraftPower Plants sponsored by the Headquarters Air Materiel Command,Wright-Patterson Air Force Base, Dayton, Ohio, on May 27 and May 28,1948.

Coatings applied in very thin layers are quite important, for example,on gas turbine blades in which distortion of the air foil cannot betolerated, in reduction of Weight of jet engine parts, and in coatingextremely thin edges, all types of welds, and combinations of variousmetal thicknesses. Thinness is also a substantial factor in betteradherence which eliminates cracking, chipping, spalling and damages doneby flying ceramic particles which may be considerable in high speed gasturbines and the like when comparatively thick coatings are used.

Accordingly, a primary object of my invention is the provision of novelsimplified methods of formulatingand compounding protective compositionsof matter which, when applied in very thin layers to metals and theiralloys, have considerably improved thermal and. mechanical shockresistance, high oxidation and corrosion resistance at very hightemperatures, and other desirable properties heretofore unattainable inprotective ceramic and enamel coatings, and which provide those skilledin the ceramic arts with wide latitude in selection of materials toproduce desired properties in formulating or compounding improvedportective layers for metals and alloys.

Another object of my present invention is to provide protectivecompositions of matter which may be simply formulated and which, whenformed on or applied to the surfaces of metals, such as iron, steel,molybdenum, nickel, chromium, cobalt, tantalum, tungsten, etc., andtheir alloys, Will provide very thin, impervious, highly refractory,corrosion and oxidation resistant layers of surface compositions whichare tightly bonded to the base material, and are of exceptionalmechanical and thermal shock resistance, and which do not materiallyincrease the Weight of the protected objects, are highly useful atnormal temperatures, and provide prolonged life at elevatedtemperatures.

A further object of my invention is to provide novel compositions ofmatter which in very thin layers give substantial protection tomaterials of the foregoing types for extended periods of service lifeagainst oxidation and corrosion above 1500 F.

Another object of my invention is to provide protective compositions ofsimplified formulation, and producible with simplified manufacturingcontrols, which may be formed on the surfaces of the material to beprotected in thicknesses of the order of .0005 to .003 of an inch, andwhich will adhere to extremely thin and raw metal and alloy edges, toall types of welds, and to combinations of various metal thicknesses,without cracking, chipping or spalling under severe mechanical andthermal shock.

It is a further object of the invention to provide a novel process forprotectively coating metallic surfaces involving the selection ofcoating material ingredients that all have substantially the samecrystal structure and which when combined and fired upon a metallicsurface develop at the metallic surface a final crystal structure thatis substantially the same as that of the normal surface layer of themetal.

A further object of the invention is to provide a novel process forcoating metallic surfaces wherein materials that possess the same orvery nearly the same crystal structure as the oxides that are normallyformed on such metallic surfaces are thermally bonded to the surfaces.

Other objects of my invention will appear from the following disclosureof preferred embodiments thereof and from the appended claims. Referringto the drawmgs:

Figures 1 and 1A comprise a tabulation of metals and ceramic rawmaterials which I have so far found available for use in the formulationof my improved protective compositions, and are illustrative of thetypes and characteristics of the materials that may be used in carryingout my invention and discovery. This tabulation indicates materials,chemical symbol, chemical grade, and crystal class of such materials,where presently known or readily available in the literature, accordingto Shoenflies system of designation. Materials are listed generallyaccording to their functions in several groups as follows:

Group I.Complex minerals which increase stability and durability ofcoatings and comprised in general of complex compounds made up ofmaterials listed in Groups 2-5, inclusive.

Group 2A.--Metals which have been used in high temperature alloys whichincrease adherence and thermal shock resistance of my improvedcompositions.

Group 2B.-Oxides of metals which have been used in high temperaturealloys which increase adherence and thermal shock resistance of myimproved compositions.

Group 3.Oxides which may be classed as partial glass network formers orwhich increase the durability of glasses.

Group 4.Oxides which are definitely known to form glasses.

Group 5.-Materials which produce fluxing action or are so-called glassmodifiers.

Figures 2 and 2A comprise a tabulation of some specific examples oftypical protective compositions formulated from materials of the variousgroups of Figure 1 in accordance with my invention and discovery,numbered consecutively for convenient reference hereinafter. Amounts ofconstituents are given by relative weight.

Figure 3 is a tabulation of illustrative examples of my best coatingapplications which have so far been formulated, applied and tested onthe various listed metals and alloys, with firing temperatures andtimes, and A. M. C. test data.

Figures 4 to 11 are photomicrographs of typical compositions formed onbase materials of A181 steel alloys 1010, 347, 310, 314; Inconel;(Vitallium); and the Allegheny Ludlum cobalt-chromium-nickel alloy knownunder the designation S816.

Figures 4 to 11, inclusive, of the drawings are reproductions of actualphotomicrographs of sections through specimens comprising a metal basehaving a ceramic coating formulated and applied thereto according to theprinciples of the present invention. These micrographs were made withplane-polarized illumination since, under light the ceramic coating,being somewhat translucent would record dimly or not at all. Due to thepolarized light, the metal in each case appears quite dark and theetched areas of the metal and grain boundaries are exaggerated as aredirt, grease, and other foreign matter.

Figure 4 is a power magnification and shows, from top to bottom, theBakelite (used to hold the specimen), the ceramic layer, areas ofdiffusion at the ceramicmetal interface, and the base metal with thedark areas being matrix and the light areas natural inclusions(sulphides, silicates, etc.). In this as well as the remaining figures,the Bakelite appearing at the top of each photograph contains lightsplotches which are ceramic and/ or abrasive particles embedded thereinduring the grinding and polishing of the specimen.

In Figure 5 (250x) the interface between the metal base and ceramiclayer shows a fairly continuous dark line, separating the ceramic layerfrom the interdifiusion zone. The light areas appearing in the metalbase are caused by etched pits. Because the ceramic is harder than themetal, it is ditficult to polish the specimens to an absolutely flatplane and, therefore, in some pictures either the metal or the ceramicis slightly out of focus. In this particular photograph, the metal issufiiciently out of focus to exaggerate the etched pits.

Figure 6 (250x) is one of the better showings of the difiusion areas.The grain boundaries are clearly outlined because the metal is veryslightly out of focus. As a hypothetical point, if, before this specimenwas etched, the layer of ceramic could have been put on the metal area,then the etch cycle completed, and the ceramic removed before thismicrograph was taken, the grain boundaries would not be visible because,noetching action could have taken place through the ceramic coating.

In Figure 7 (100x) is also a good showing of the diffusion layer joiningthe ceramic coat and metal base.

In Figure 8 (100x) the metal is slightly out of focus and therefore theinner metallic compounds are exaggerated but the ceramic coating showsquite clearly.

Figure 9 (100x the ceramic is slightly out of focus while the metal iswell in focus with good grain boundary delineation. As a result thediffusion area is not too obvious. It is to be understood, however, thatwhile as in this photograph, the laminar zone of interdiifusion betweenmetal and ceramic does not record obviously in all the photographs ascompared, for example with Figure 6, this interdiffusion existed in allspecimens tested.

Figure 10 (100x) shows, as can be seen by the spotty appearance of themetal, one of the super alloys such as N-l55 and 8-816, theinterditfusion zone being clearly delineated at the interface althoughnot so well defined as in Figure 6.

In Figure 11 as in Figure 9 the area of interditfusion is notparticularly well defined. However, both coat and metal are in excellentfocus and the interface is particularly clear.

As best appears in Figure 6, it will be seen that the fired coatings ofmy invention form a layer bonded to the base metal by a laminar zone ofinterdiifusion of the ceramic and base materials. It has been found thatthe interdifr'used layer at the interface remains even when the primaryor external coating has been spalled off and that said interdiffusedlayer provides a substantial degree of protection for the base material.Thus it will be appreciated that a coated base is composed of threelayers, namely, a first or structural layer consisting entirely of thebase metal; a second or outer layer which is purely ceramic in nature,vitreous in appearance and crystalline or cryptocrystalline instructure; and, at the interface of the base metal and the coating, athird lamination cou- 5 sisting :of interdiffused crystals of base andcoating materials.

In other words a bond between the metal and coating is achieved by meansof atomic lattice interfitting between the crystals thereof, the thirdlamination being in fact a combined bonding layer and secondaryprotective layer.

The basic concept of my invention comprises the discovery that it ispossible to methodically, accurately and predictably select ingredientsto be combined and fired in thin layers upon metallic surfaces, whichcombinations of ingredients develop in the final thermally bonded layera crystalline or crypto-crystalline structure that is optimum forcombination with the metallic surface. My understanding is that there isdeveloped in the fired layer a crystal or like structure of suchatomicspace grouping as to have good lattice interfit with the crystalstructure of the metallic surface. I have ascertained that any of alarge number of ingredients are available for substitution in thecombination in place of any of the ingredients, the substituteingredients having similar crystal space groups, so that ingredients ofthe layer to be applied to a given metallic surface may be selected bythose skilled in the ceramic arts and put together on the foregoingbasis with due consideration for all special requirements of the finalproduct to produce layers that are known to have maximum adherence andoptimum protective values.

Incarrying out the invention according to its preferred embodiment, Istrive to replace the normal oxide coating of the metallic surface witha protective layer of superior properties. Hence the preferred techniqueis to select those-ingredients which possess the crystal space groupingthe same or nearly the same as the normal oxides, and whichalso areselected for the type of protection desired. Thecombination ofingredients is completed by this process of selection and then firedupon the surface. If different properties are required for certainconditions of operation, ingredients of appropriate properties may besubstituted on the foregoing basis of related crystal structure.

With regard to the following disclosure, my present improved methods offormulation and my improved compositions are formed on my discovery thatby utilization of the ceramic materials outlined in Figures 1 and 1A,crystalline or cr'ypto-crystalline protective compositions are developedon firing which have good lattice fit between the protective surfacelayer and the metal or alloy to be protected, which are noveland"have.greatly improved protective qualities on the surfaces of thebase materials, and which have highly useful, new and improvedproperties. For example, in treating oxidation resistant metals andalloys, I can form very thin surface layers of new protective materialshaving considerably improved refractoriness and oxidation resistancecompared to the normal oxide films on such metals and alloys. Myimproved compositions may be combinations with such normal protectivefilms to produce better ones, or may replace them, and can be applied asprotective layers or films on base materials whose normal oxide coatingsdo not inhibit oxidation.

In carrying out my invention, I utilize mixtures of materials tabulatedby groups according to function in Figures 1 and 1A and selected fromthe groups depending upon the coating characteristics desired. Theseselected materials are mixed in combinations, which when applied in thinlayers to the metallic base materials to be protected and properly firedas hereinafter set forth in detail, develop crystal orcrypto-crystalline structures having one or more axes comparable to thecrystal axes of the base materials. As a result of extensive tests andexperience with my improved compositions and their new and superiorproperties, I have developed a simplified theory that certain materialsincluding those listed combine on firing to form solid solutionscontaining crystals with atomic spacings the same, or nearly the same,as that along the crystal edges of the base materials. And that bindingof the protective layer to the base material is due to the lattice fitthrough the residual valence electrons or a rapid exchange of theelectrons between the atoms of the protective layer and the freeelectrons in the base material. It is also my theory that electrostaticattraction may increase the bonding energy butthat the union between myimproved protective layer and the base material is more than likelysomewhere between ionic and metallic, and consequently a homopolar orvalence bond.

In any event, in accordance with my discovery and invention, I producenew outer protective layers on the base materials havingvarious new andimproved properties not present in prior protective coatings, includingsuperior corrosion, mechanical and thermal shock resistance, and alsosuperior bonding to and union with the base material. In many instancesmy improved protective layers may be hammered Without chipping orspalling.

In carrying out my invention, I have discovered that the metal andceramic constituents used to formulate my improved coatings may beclassified in general under the first three of the six systems ofcrystallization outlined in W. E. Fords fourth edition of Danas Textbookof Mineralogy. These include the isometric, tetragonal and hexagonalsystems. Also, that the majority of the available materials fall in thenormal class of each system which contains crystals exhibiting thehighest degree of systems have also been used as constituents to producesatisfactory compositions, but in all such cases the protective qualityand life of the coating is reduced below those attainablein my bettercoatings. The space groups of thematerials used to formulate my improvedprotectivecompositions as indicated by the symbols of the Shoenfliessystem in the X-Ray Crystallographic Data section of the Handbook ofChemistry and Physics, 31st edition, 1949, are as follows:

4 5 7 a 14 19 2 4 6 4 4 h) O11) O11; hr lln D4117 fih; 6h: 3d: D3) 06V!and Space groups for many complex minerals classified in Figures 1 and1A according to function in Group 1 and space groups for some glassforming network materials in functional Group 4 are presently unknown ornot readily available in published literature but it is believed thatthey can be identified with the crystallographic sys terns and classesas outlined.

In applying my discovery and invention to the formulation and productionof my basic improved protective compositions, materials are usuallyselected from the first two or three groups tabulated in Figures 1 and1A, applied to the metal or alloy to be coated and fired. Alterationsand substitutions based on tests are then made, using, if necessary,other materials selected from any of the five groups on the basis ofsimilar crystal space grouping, until the optimum protective layer forthe particular purpose is obtained. Excellent protection has beenobtained with layers formulated with materials from two or more groupsbecause tests indicate that all mixtures apparently combine upon firingto develop an atomic spacing, along an edge of the crystal lattice, thesame, or nearly the same, as that along the edge of the crystal of themetal or alloy being coated.

Selection of materials used in coatings is in general governed by theirfunctions outlined above in the brief description of the drawings, theenvironment in which protection is required, and the type of coatingdesired. For example, to increase adherence and thermal shock resistanceof my protective compositions, I add a material selected from Groups 2Aand 2B. To increase stability and durability I add specific ceramiccompounds from Group 1 or materials from Group 3. To obtain morevitreous or impervious coatings I add materials from Groups 4 and 5. Ican also control the properties of coatings by selecting and addingmaterials from any group to produce chemical resistance; coatings whichdo not attack the base metal or oxidation and corrosion resistantcoatings to fit most engineering requirements. When necessary ordesirable, I limit oxide formation on the base material by controllingthe furnace firing atmosphere.

In the formulation of protective layers having specified properties forspecific materials, in accordance with my invention, samples of thematerial to be protected may be used in sizes depending upon materialavailability. Samples 2 x 4 inches, 1 /2 x 3 inches and /2 x 1 inch areordinarily used for metals and alloys. The materials to be used in theformulation of the protective layer are selected according to functionand crystal space grouping from Figures 1A and 1B of the drawings. Nospecial preparation such as fritting is required. The mixture need onlybe ground to the fineness required.

After mixing, water and a suspension agent are added, and the mixturemilled to produce a slip of the fineness desired. Most of myformulations require only about one hour of milling, although the timemay be more or less, depending upon the ingredients and their hardness.After milling, the slip is adjusted by adding or removing water toprovide a viscosity suitable for dipping, spraying, or slushing onto thebase material. Application by spraying is preferred because this methodprevents beading and permits more uniform thickness. No specialpreparation of the metal or alloy to be protected is required, exceptthat it be free of dirt, oil and excess scale, a condition readilyobtained by sandblasting to mention one of several methods known tothose skilled in the art.

After coating, the samples are furnace or air dried and then fired for aperiod of time and temperature dependent upon the base material and themixture used and determined by experiment. Coatings are then checked foradherence and thermal shock resistance and tested. Mechanical bendingand hammering are used to check adherence and water quenching to roomtemperature from 1600 F. to 2000 F. to determine thermal shockresistance. Compositions which exhibit desired properties under suchtreatment are then tested, using the tentative Air Materiel Commandceramic coating test which comprises 72 hours of alternate heating andair quenching and soaking at contemplated operating temperatures.Included are a cyclic heating period for fifteen minutes followed by anair quench every half hour for an eight hour period and then a sixteenhour soak re peated each day until seventy-two hours have beencompleted.

All compositions listed in the formula chart, Figures 2A and 2B, areuseful in differing applications, and will pass at least five hours ofthis test. Additional protective life and other desired characteristicsare obtained by substitution of materials in specific basic formulae andrepeating the processing of coating, firing and testing in a manner wellknown to those skilled in the art, until compositions are determined,which will give the desired life and characteristics required for aspecific application.

By way of specific example, composition S-5 of Figure 2 is an excellentbasic mixture for the protection of metals and alloys, and whenformulated in accordance Beryl Si SIC These materials are mixed with asuitable quantity of water and a suspension or thickening agent, such ascitric acid, Ca(NO methyl cellulose, or the sodium salt of polymerizedd-mannuronic acid known as Kelgin LV, and milled to a fineness suitablefor spraying, dipping, slushing or brushing, depending upon theapplication and the thickness of the coating required or desired. Theresulting slip is then applied to the prepared metal, for example, A. I.S. I. (S. A. E.) No. 1010 steel and fired at a temperature of about 2200F. for about 10 minutes. The suspension agent used is not critical andmay be any water soluble dispersing agent known to those versed in theceramic arts which produce hard, tough and flexible films on drying.Firing time and temperatures vary and depend upon size of sample, gauge,etc.

A controlled atmosphere firing of the coating results in a smoother,better coating than otherwise and for some applications is quiteimportant. For control, depending upon the base material coated, aslightly oxidizing, neutral, or reducing atmosphere may be used or thefurnace atmosphere diluted with an inert gas. In some cases, betterresults are obtained in ordinary furnaces by using a suitable metalcontainer or box to enclose the coated part and flushing the box withinert gas during firing. Although any inert gas appears to givesatisfactory results for control purposes, I prefer to use nitrogenbecause of ready avaliability and lower cost. While the end result is acombination of coating formula and atmosphere, the firing technique orcoating composition may be easily altered to fit practically all furnaceconditions by those skilled in the art, and permits satisfactorycoatings to be applied to any of the rapidly oxidizable metals Withoutthe coatings spalling, fishscaling or blis tering. With proper control,the thickness of normal metal or alloy oxides may be limited to providea better, more uniform surface bond. For rapidly oxidizable metals, suchas molybdenum, iron, Hastelloy B (a Haynes Stellite Company alloy whosenominal composition is Ni 65.1%, Mo 28.6%, Fe 4.7%, C .05%, Mn 59%, andSi .19%), etc., the normal oxide is kept to a minimum during the firing,otherwise the coating Will spall or flux off.

The above formula is, of course, merely illustrative and the ranges andceramic materials may be varied Widely. For example, oxidation testswith iron as the base material at 1600 F. for extended periods show thatsatisfactory oxidation resistance and adherence is ob tained usingcoating S5 throughout the following ranges by Weight:

Beryl Si SiC As will be seen from the charts, Figures 1, 1A, 2 and 2A,certain substitutions may be made in this formula, provided the crystalspace groups are the same, or nearly the same, preferably those in thesame class or those that exhibit the next lowest order of symmetry. Asanexample, nickelous oxide or cobaltic oxide may be substituted forsilicon, and zinc oxide or beryllium oxide may be'substituted forsilicon carbide. Since the available crystalline space group andcrystallographic data of complex ceramic compound similar to beryl islimited, the full range of substitute materials cannot presently beselected on the basis of crystal space lattice, but I have 9 determinedby experiment and test that mullite (3Al O .2SiO potassium feldspar (KO.Al O ;6SiO zinc zirconium silicate (ZuO.ArO .SiO and others listed inthe complex mineral Group 1, Figure 1, may be used.

I have also determined that the Wide range of ceramic substitutionspermits some contamination and variations in the grades of the materialsto be used without resultant deterioration of coating. For example,thin, strong, tightly adhering, thermal shock resistant compositionshave been-developed by using reagent, chemically pure, technical andcommercial gradematerials. This latitude does much to simplify thecontrol andformulation of my improved protective compositions'forspecificuses; In addition, byproper selection of materials, those whoare familiar with the ceramic art can alter firing times andtemperatures to meetspecific conditions. For the compositions disclosedherein, it has been determined that the firing time will vary from twoto twenty minutes'and firing-temperature from1500" F. to 2600 F., asindicated for some compositions in the tabulation of Figure 3.

The wide range of acceptable materials permitsmy basic protectivecompositions to be altered to develop more or less refractoriness, morevitreous impervious surfaces,- and resistance to chemical attack bytheproper selection of ceramic materials; I have-also discovered thatmy'improved basic compositions may be combined and/or fired in variouscombinations.

For example, I have discovered that a more impervious composition thancoating S- results by the addition of one part by weight of titaniumdioxide, which does not detract from the basic coating qualities. Such amore impervious composition (S-7 of Figure 2) by way of example consistsessentially of the following parts by weight;

Beryl Si SiO T102 These materials are mixed, applied and firedin thesame manner as the basic ceramicmixture, except that firingrfor fiveminutes at ate'mperature of2200" Fgis required.

I have also foundthat tin oxide or zircon may be sub- I have determinedthat the-best results are obtained ifthe metal added forms an oxide of-high melting point of suitable crystal space group that will fit thecomposition.

A more vitreous coating can be'obtainedby includ-' ingknownglass'networkformers of proper-crystal-space gr'oupand the addition of aflux or so-called glass modifier" of proper crystal space group. Testsshow that if t a coat ing formula is compounded to included SIO ,P O orB 0 along with other ceramics selected according to my invention anddiscovery and lithium fluoride, sodium fluoride, or potassiumfiuoride'are added, a glassy or vitreous surface is formed. A typicalexample is coating 8-28 (Figure 2A) which consists essentially of thefollowing parts by weight:

I Beryl I Z1 01 I s I 2 These materials are mixed, applied and fired inthe same manner as the basic ceramic mixture, and fired for five minutesat a temperature of'2150 F.

it Asshown by thecharts, UP and NaF belong int he crystal space group,but I have found by test that ceramics with crystal space group Beryl SiA1201 B60 TiOz and coating S-28 (Figure 2A) consists essentially of thefollowing parts byweight:

I Beryl ZrOz I $102 I 13203 I Bo LiF NaF I I 8 2 s 2 I 2 1 I 2 I (1)Both may be applied and fired directly on metals and ll their"alloys toproduce satisfactory protection compositions' (2) or S-12 may beappliedand fired as a base, and then'S-iZS appiied andfired as a top coating,(3) or S-l2 may be applied and thenS-ZS applied and both fired together,(4-) or S-12 may be mixed with S28 to produce coating S 40consistingessentially of-the following parts by weight:

Be'r iI siIzroz sioiIaroa A1203 BeO rioiilmr INaF 16' 4 2 8 2 s 4 a v1'2 compositions to be mixed or highly refractory top compositions to beadded in a manner somewhat similar to that used for vitreous coatings.For example, the =refrac' toriness of coating, S-8 which consistsessentiallyof the following .parts by weight:

maybeincreasedby adding atop layer ofi coating S -8Tl which consistsessentially of the following parts by weight:

. ZrOr- S1 02 A1203 B These .coatings -may be applied and fired usingthe same technique as that for developing more vitreous coatings, exceptthat some highly refractory top coatings cannot be fired directly uponthe metal or alloy.

The chemical resistance of the materials that may be used in coatingformulation also permits formulation of compositions in accordance withmy invention with added chemical resistance and without deterioration inbasic composition properties. For example, by incorporating only acidresistant materials in the coating, high temperature, acid resistantcompositions may be fired on metals and alloys to provide base materialprotection.

My improved compositions may also be fritted in a manner similar to thatused in the enamel art, by mixing and smelting at temperatures from 1700F. to 3000 F. until maturity is indicated by the ability to draw asmooth glass thread from the batch. The smelt is then quenched bypouring it into Water and then it is dry or wet ground to the finenessdesired for spraying, clipping or slushing. This process imparts moreuniformity and higher refractoriness to some coatings, but is seldomrequired and is described to illustrate the wide flexible range ofinherent mixture properties when the coatings are formulated byselection of materials in accordance with my invention and discovery.

All of the numerous formulations in accordance with my invention anddiscovery so far tested give improved protective results on all metalsand alloys so far tried. Lack of time and facilities have prevented thetesting of all available metals and alloys'with my protective coatings.However, tests conducted over the past several years show that by theproper selection of materials in accordance with my invention anddiscovery, protective layers may be speedily formulated and fired onmetals and alloys to meet the most exacting requirements. To date,layers of protective composition have been produced for truck exhaustmanifolds, burner cups, gas turbine combustion chamber liners,transition liners, nozzle diaphragms, gas turbine and compressor blades,rocket motors, and ram jets. Metals and alloys, including molybdenum,tungsten, tantalum, S. A. E. steels 1010, 1020, 4130, and 6323,Stainless steels Standard Type Nos. 406, 430, 501, 302, 321, 347, 310and 314, Inconel (Ni 80%, Cr 14%, Fe 6%), Vitallium (Cr 25%, Co 69%, Mo6%, C 24%) and Hastelloy B (Ni 65.1%, Mo 28.6%, Fe 4.7%, C .05%, Mn.59%, Si .19%) have all been successfully protected by improvedcompositions, and the experience so far had with the foregoing widevariety of metals, alloys and articles subjected to very hightemperatures indicates that satisfactory protecting composition for manyother metals, alloys and services can be formulated in accordance withmy methods herein disclosed. Also by my invention tightly adhering,thermal shock resistant, vitreous protective surface layers may beproduced on carbon, graphite, titanium carbide, silicon carbide and thelike.

A partial list of the base materials, compositions used, firing timesand temperatures, composition thicknesses, and Air Materiel Command (A.M. C.) data is given in the tabulation of Figure 3 of the drawings.

It will accordingly be seen that materials with the foregoingproperties, selected and applied to the base materials in accordancewith my invention, combine to form thin, flexible, tightly adhering,protective layers that materially extend the normal life of metals oralloys at temperatures, and in corrosion and oxidation environmentswhich produce rapid failure of the unprotected base materiahand openvast new possibilities of mechanical design and improvement in hightemperature equipment. The best of these compositions are applied invery thin layers of the order of .0005 to .003 of an inch, have a widerlatitude of coating formulation, better adherence, better mechanical andthermal shock resistance, and have other desirable properties heretoforeunobtainable with prior enamels and ceramic coatings.

This application is a continuation of pending application 3. N. 133,045,filed December 15, 1949 for Com- 12 positions of Matter and Methods ofTheir Production, now abandoned.

Certain terminology used in the claims is defined as follows: (1) Theexpression in the claims of materials in Group 1, and like expressionsrelating to Groups 2, 3, 4 and 5, refer respectively to all thematerials listed in corresponding Groups 1, 2, 3, 4 and 5 in Figures 1and 1-A of the drawings in this application (and such equivalentsthereof as may fairly fall within applicants disclosure under the patentlaw doctrine of equivalents). (2) The word essential used in the thirdlast clause of process claims numbers 12-17 is not intended to includemill additions.

The terms fire bonded and firing used in the claims are not limited toheating the base metal and ceramic coating through the directapplication of fire to bond the coating to the base metal, but includealso indirect heating, as for example, heating in a furnace or the like.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. An article of manufacture comprising a metallic body having acrystalline structure, and a ceramic coating havinga continuous surfaceconsisting essentially of a crystalline or crypto-crystalline structurefire bonded on said body, said coating having a crystalline interlockedpermanent bond with said metallic body.

2. An article of manufacture comprising: a metallic body having acrystalline structure; a ceramic coating having a continuous surfaceconsisting essentially of a crystalline or crypto-crystalline structurefire bonded on said body; and a laminar zone of interdiffused particlesof base metal and ceramic coating at the interface between said coatingand body.

3. An article of manufacture comprising: a metallic body having acrystalline structure with at least its principal constituent havingunit cells of the cubic and hexagonal classes; a ceramic coating having'a continuous surface consisting essentially of a crystalline orcryptocrystalline structure fire bonded to said body, said coatingconsisting of at least two materials having a crystal structure of thecubic, hexagonal and tetragonal classes; and a laminar zone ofinterdiffused crystals of base metal and ceramic coating at theinterface between said ceramic coating and metallic body.

4. An article of manufacture comprising: a metallic body having acrystalline structure; a ceramic coating having a continuous surfaceconsisting essentially of a crystalline or crypto-crystalline structurefire bonded to said body, said coating consisting of at least twomaterials each from the group consiting of those having the spacegroupings of and 6 6 4 4 19 311; 3d; 3: 6V1 2V ing a continuous surfaceconsisting essentially of a crystal-' line or crypto-crystallinestructure fire bonded to said body, said coating consisting of at leasttwo materials; one of .said two materials bs'ingfrom one of Groups 1,2,'3,54 and of Figures 1 and 1A, and the other of said two materialsbeing .from one of the other 3 of said groups; and a laminar Zone ofinterdiifused crystals of base metal and ceramic coating at theinterfacebetween said ceramic coating and metallic body.

61 An article of manufacture as defined in claim 1, wherein the. totalthickness of said coating and laminar zone is less than 0.003 of aninch.

7. An article ofmanufacture comprising: a metallic body having acrystalline structure; a ceramic coating having a continuous surfaceconsisting essentially of a crystalline or crypto-crystalline structurefire bonded on said body; and a laminar zone of interdiifused particlesof base metal and ceramic coating at the interface between said coatingand body; said coating consisting principally of one or more ingredientshaving a crystal structure of the cubic, hexagonal and tetragonalclasses with an atomic lattice spacing that is substantially an integerof the lattice spacing of the principal material of said metal body.

8. An article of manufacture comprising: a metallic body having acrystalline structure with at least its principal constituent havingunit cells of the cubic and hexagonal classes; and a ceramic coatinghaving a continuous surface consisting essentially of a crystalline orcrypto crystalline structure fire bonded to said body, said coatingconsisting of at least two materials having a crystal structure of thecubic, hexagonal and tetragonal classes, said coating having acrystalline interlocked bond with said metallic body.

9. A process of ceramic coating a metallic base that has a crystallinestructure with at least its principal constituent having unit cells ofthe cubic and hexagonal classes, comprising the steps of: compoundinginto a slip as principal ingredients thereof a mixture of at least twomaterials each having a crystalline structure with unit cells of thecubic, hexagonal and tetragonal classes; applying said slip to saidmetallic base; and firing it until a ceramic coating consistingessentialy of a crystalline or crypto-crystalline structure ispermanently bonded there- 10. A process of coating a metallic base witha ceramic coating of crystalline or crypto-crystalline structurecomprising the steps of: compounding into a slip as principalingredients thereof a mixture of at least two materials, one of saidmaterials being selected from one of Groups 1, 2, 3, 4 and 5 in Figures1 and 1A and the other of said materials being selected from one of theothers of said groups; applying a layer of said slip to said metallicbase; and firing it until a ceramic coating consisting essentially of acrystalline or crypto-crystaline structure is permanently bondedthereon.

11. A process of ceramic coating a metallic base that has a crystallinestructure with at least its principal constituent having unit cells ofthe cubic and hexagonal classes, comprising the steps of: compoundinginto a slip as principal ingredients thereof a mixture of at least twomaterials each having a crystalline structure with a space lattice ofthe 4 5 7 9 14 19 2 6 4 4 19 h, h; h; h: 11; 11: 61]; 3d: 37 6V; 2V

and

classes according to the Shoenflies system of identification; applyingsaid slip to said metallic base; and firing it until a ceramic coatingconsisting essentially of crystalline or crypto-crystalline structure ispermanently bonded thereon.

12. A process of ceramic coating a metallic base comprising the stepsof: compounding a protective coating one or more ingredients selectedfrom the materials in Group 5; making a slip including said compositionas theessential component thereofiapplying said slip to said base; andfiring it toform a ceramic coating on said base.

13. A process of ceramic coating a metallic base comprising the stepsof: compounding a protective coating composition comprising a mixtureconsisting essentially of about 820 parts by weight of one or moreingredients selected from the materials in Group 1; about /s--6 parts byweight of one or more ingredient sselected from the materials in Group2; about 522 /2 parts by weight of one or more ingredients selected fromthe materials in Group 3; about 2-10 /2 parts by weight of one or moreingredients selected from the materials in Group 4; and about 1-7 partsby weight of one or more ingredients selected from the materials inGroup 5; making a slip including said composition as the essentialcomponent thereof; applying said slip to said base; and firing it toform a ceramic coating on said base.

14. A process of ceramic coating a metallic base comprising the stepsof: compounding a protective coating composition comprising a mixtureconsisting essentially of about 6-12 parts by weight of one or moreingredients selected from the materials in Group 1; about 4-12 parts byweight of one or more ingredients selected from the materials in Group3; about 4-14 parts by weight of one or more ingredients selected fromthe materials in Group 4; and about 1-8 parts by weight of one or moreingredients selected from the materials in Group 5; making a slipincluding said composition as the essential component thereof; applyingsaid slip to said base; and firing it to form a ceramic coating on saidbase.

15. A process of ceramic coating a metallic base comprising the stepsof: compounding a protective coating composition comprising a mixtureconsisting essentially of about 8 parts by weight of one or moreingredients selected from the materials in Group 1; about 4-24 parts byWeight of one or more ingredients selected from the materials in Group2; and about 4-16 parts by weight of one or more ingredients selectedfrom the materials in Group 3; making a slip including said compositionas the essential component thereof; applying said slip to said base; andfiring it to form a ceramic coating on said base.

16. A process of ceramic coating a metallic base comprising the stepsof: compounding a protective coating composition consisting essentiallyof about 8-12 parts by weight of one or more ingredients selected fromthe material in Group 1; about /2-8 parts by weight of one or moreingredients selected from the materials in Group 2; about 16-23 parts byweight of one or more ingredients selected from the materials in Group3; and about 8-14 parts by Weight of one or more ingredients selectedfrom the materials in Group 5; making slip including said composition asthe essential component thereof; applying said slip to said base; andfiring it to form a ceramic coating on said base.

17. A process of ceramic coating a metallic base comprising the stepsof: compounding a protective coating composition consisting essentiallyof about 8 parts by weight of one or more ingredients selected from thematerials in Group 1; and about 20 parts by weight of one or moreingredients selected from the materials in Group 3; making a slipincluding said composition as the essential component thereof; applyingsaid slip to said 15 base; and firing it to form a ceramic coating onsaid base.

18. A protective coating composition comprising a mixture consistingessentially of about 8-20 parts by Weight of one or more ingredientsselected from the materials in Group 1; about %6 parts by Weight of oneor more ingredients selected from the materials in Group 2; about 522 /zparts by Weight of one or more ingredients selected from the materialsin Group 3; about 2-10 /z parts by Weight of one or more ingredientsselected from the materials in Group 4; and about 1-7 parts by weight ofone or more ingredients selected from the materials in Group 5.

References Cited in the file of this patent UNITED STATES PATENTS RavaMay 12, Lucas Nov. 3, Emery Feb. 16, McIntyre June 15, Cooper Dec. 21,Long Dec. 25, Deyrup Apr. 12, Bennett et a1. July 5,

FOREIGN PATENTS Australia June 24,

1. AN ARTICLE OF MANUFACTURE COMPRISING A METALLIC BODY HAVING ACRYSTALLINE STRUCTURE, AND A CERAMIC COATING HAVING A CONTINUOUS SURFACECONSISTING ESSENTIALLY OF A CRYSTALLINE OR CRYPTO-CRYSTALLINE STRUCTUREFIRE BONDED ON SAID BODY, SAID COATING HAVING A CRYSTALLINE INTERLOCKEDPERMANENT BOND WITH SAID METALLIC BODY.